1. Field of the Invention
The invention concerns copolymers of .alpha.-.beta.-unsaturated dicarboxylic acid esters with .alpha.-olefins, their production and their use.
2. Description of the Prior Art
Olefin-maleic acid-copolymer derivatives are known from German Offenlegungsschrift DE-OS 2,727,329, which are constructed from olefins with an average of 2-24 carbon atoms and maleic acid and are converted into esters with monovalent alcohols having a chain length from 2-20 carbon atoms in a mole ratio 1:0.5 to 1:2 maleic acid to alcohol. The there described olefin-maleic acid-copolymer derivatives are produced through copolymerization of maleic acid anhydride with .alpha.-olefins and subsequent esterification into semi- or diesters. The there described olefin-maleic acid-copolymer derivatives are particularly suitable for the lubricants in the shaping treatment of synthetics, i.e. plastics. These products are semi-solid to solid at room temperature. Their pour point always lies clearly above 0.degree. C.
In other respects, high-molecular copolymers from .alpha.-olefins and from .alpha.-.beta.-unsaturated dicarboxylic acid esters have been known, for example as hair sprays (AU-PS 254,327) and as agents for the coating of medicines (AU-PS 263,011). These were produced through copolymerization of .alpha.-olefins and .alpha.-.beta.-unsaturated dicarboxylic acids or acid anhydrides and supplementary esterification of the copolymers, and are wax-like to solid at room temperature.
A copolymer of a C.sub.22 -C.sub.28 -1-olefin and dibehenylmaleate is known from German Offenlegungsschrift DE-OS 1,770,860, and is obtained by polymerization at 150.degree. C. It is described as a wax-like product. It was suggested to mix hydrocarbons with the product, in order to lower the pour point or altogether to improve the flowability.
In DE-OS 1,770,860 it is set forth that the flowability improvement can only be obtained with such ester-polymers in which the number of carbon atoms in the alkyl part of the ester amounts to more than 20.
Flowability improvers for wax-like hydrocarbon oils are described in AU-PS 479,746, which effect a lowering of the pour point of the hydrocarbon-oil. Here also, expressly long side chains for the alcohol component of the dicarboxylic acid esters have been described as unconditionally necessary. The consistency of the product at room temperature is wax-like to solid. The pour point thus here also lies clearly above 0.degree. C.
U.S. Pat. No. 2,615,845 to Lippincott et al. describes a copolymer of an unsaturated dicarboxylic anhydride and various olefins of chain lengths from C.sub.3 to C.sub.18, which can be esterified with alcohols of chain length from C.sub.2 to C.sub.14 ("Lorol B"). Lippincott presents pour point data in its examples, but the measurements given are for a copolymer-test oil mixture, not the pure copolymer itself.
U.S. Pat. No. 3,314,908 to Kagan et al. teaches the use of C.sub.4 to C.sub.9 olefin in the copolymer and is concerned with the preparation of tough, flexible solids suitable as paint vehicles.
Japanese Publication 157687/1980 (Mitsubishi) discloses copolymers of C.sub.4 to C.sub.18 .alpha.-olefins and .alpha.-.beta.-unsaturated dicarboxylic acid esterified with C.sub.1 to C.sub.18 alcohols. Mitsubishi shows a pour point as low as -18.degree. C. with a C.sub.8 alcohol esterifying agent and .alpha.-olefin chain length of C.sub.16 -C.sub.18. Higher pour points are shown or implied for combinations of other olefins and esterifying alcohols.
U.S. Pat. No. 2,543,964 (Glammaria) discloses copolymers of olefins up to C.sub.30 chain length and polybasic acids esterified with alcohols having "as few as twelve or perhaps even fewer carbon atoms" but data is not given for any alcohol lighter than C.sub.12.
The above described prior art illustrates that lubricating oils have been sought for a long time which display a low pour point without additives, and which have a smallest possible viscosity variation over a broadest possible temperature range. However, the prior art does not provide knowledge of a family of particular .alpha.-olefins and esterifying alcohols having specific ranges of carbon chain lengths which when used in combination consistently provide desirable low pour points.